This invention relates to an anti-siphon device for preventing the siphoning of liquid fuel from a fuel tank. More particularly, the present invention relates to an anti-siphon device for preventing the siphoning of gasoline from a gasoline tank, which device is designed for permanent installation within the fuel filler pipe of motor vehicles, especially buses and trucks.
In the past, various devices have been used for preventing the unauthorized siphoning of gasoline. One such device is illustrated by the U.S. Pat. No. 2,496,992 wherein a cone-shaped spring is attached near the outer rim of a gasoline intake or filler pipe. U.S. Pat. No. 2,017,837 discloses another type of cone-shaped spring device wherein the cone is located away from the outer rim of the filler pipe. U.S. Pat. No. 3,985,259 discloses a one-piece spring, coiled in a cylindrical shape having a lower cone shaped portion, wherein the lower end of the cone is provided with a bend so that the contiguous coil portion at the lower end of the spring projects outwardly at an angle approximately 45 degrees from the vertical axis of the device.
None of these devices, however, has been found to be entirely satisfactory for the intended purpose, as the placement of such a spring or coil arrangement within the intake opening has caused sufficient blockage of the filler pipe to impede the flow of gasoline into the tank during the filling operation. The back-flow of gasoline thus created by the location of the anti-siphon device within the filler pipe causes the spillage of a considerable quantity of fuel which is a highly undesirable result. Also, many such spring devices are flimsy and can be forced out of the filler pipe into the tank by thrusting a rod or the like into the filler pipe.